Mechanics of breathing I Flashcards
What do changes in lung volume induce?
→ Changes in alveolar pressure which generate pressure gradients between alveoli & atmosphere, causing air to flow.
How does inspiration occur?
→Diaphragm contracts & thoracic cavity expands. →Alveolar pressure decreases
How does expiration occur?
→Diaphragm relaxes (and lung recoils).
→Thoracic cavity volume decreases
→ alveolar pressure increases
At the end of expiration why is there no movement of air?
→Palveoli = Patmosphere
During inspiration what happens in terms of pressure?
→The outer surfaces of the lung are pulled outwards
→ ↑volume
→ ↓alveolar pressure.
→Palveoli < Patmosphere
→Air flows from high (atmosphere) to low (alveoli) pressure.
During expiration what happens in terms of pressure?
→Air within the lung is compressed.
↓volume = ↑alveolar pressure.
→Palveoli > Patmosphere
→Air flows from high (alveoli) to low (atmosphere) pressure.
What is the pleural cavity?
→fluid filled space between the membranes (pleura) that line the chest wall and each lung.
What do pleurae provide?
→a frictionless surface to aid movement of the lungs.
What decreases the pressure within the pleural cavity?
→The opposing elastic recoil of the chest wall (outward) and lungs (inward) generates negative pressure within the pleural cavity
What does negative pressure do to the pleurae?
→Negative pressure acts to pull the two membranes together
What are the criteria for the lung volume to remain constant?
→At the end of expiration, the system is in equilibrium:
→If the force pulling the visceral pleura inwards (lung recoil) = the force pulling the visceral pleura outwards (negative intrapleural pressure)
→lung volume will remain constant.
How does the lung expand in relation to interpleural membranes?
→During inspiration, muscular contraction pulls the parietal pleura outwards
→stretching the cavity
→decreasing intrapleural pressure
→As the intrapleural pressure becomes more negative, →the force pulling the two pleurae together increases. →When this force becomes greater than the force generated by the elastic recoil of the lung
→the visceral pleura will be pulled outward
→expanding the lung
How does the intrapleural pressure increase during passive expiration?
→During (passive) expiration
→relaxation of contracted respiratory muscles
→reduces the outward force acting on the parietal pleura →reducing the cavity stretch
→ increasing intrapleural pressure
How is lung volume decreased in relation to intrapleural pressures?
→When the increased (less negative) intrapleural pressure does not generate sufficient force to overcome the elastic recoil of the lung
→ the visceral pleura will be pulled inward (along with the pleural cavity and parietal pleura)
→decreasing lung volume
During forced expiration why is there a more rapid decrease in lung volume?
→During a forced expiration
→Contraction of other respiratory muscles (such as the abdominals and internal intercostals) acts to provide further inward force on the parietal pleura
→ compressing the pleural cavity (further increasing PIP) →forcing an increased and more rapid decline in lung volume.